Low temperature distillation of normally gaseous substances



Nov. 9, 1965 G. KESSLER 3,216,206

LOW TEMPERATURE DISTILLATION OF NORMALLY GASEOUS SUBSTANCES Filed Nov. 28, 1962 N L, In vcnfor GODEHA R07 KESSLER 5y mm W A/fome75 United States Patent 3,216,206 LOW TEMPERATURE DISTILLATION 0F NORMALLY GASEGU SUBSTANCES Godellardt Kessler, Strasslach, near Munich, Germany,

assignor to Gesellschaft fiir Lindes Eismaschinen Alrtiengesellschaft, Hollriegelskreuth, near Munich,

Germany Filed Nov. 28, 1962, Ser. No. 240,667 (Ilaims priority, application Germany, Nov. 29, 1961,

9 Claims. (CI. 62-13) This invention relates to a method and apparatus for the low temperature distillation of normally gaseous substances, particularly for obtaining oxygen, preferably compressed gaseous oxygen, and simultaneously other liquid products by fractionation of liquid air in a double rectification column, with circulating nitrogen being utilized as a heat transfer medium. More particularly, the liquefied oxygen may be removed in the liquid state from the sump of a low pressure column, or it may be brought to the required pressure and gasified by heat from the circulating nitrogen.

The previously known methods of fractionating air have the disadvantage in that it has not been possible, Without the use of supplemental refrigeration or further expenditure of energy, to obtain other components from the air in a high state of purity simultaneously with the production of gaseous compressed oxygen. In these previous methods, such as that disclosed in German Patent 921,809, the compressed circulating nitrogen which was cooled and liquefied by an auxiliary cooling source, is expanded to an intermediate pressure, and a gaseous portion of the partially decompressed nitrogen is then used to heat a supplementary column for the production of a certain portion of especially pure oxygen, the nitrogen being passed into the pressure column for further expansion. By the removal of liquid fractions, their latent heat must also be removed, which, of course, involves a further expenditure of energy which burdens the industrial efliciency of the process.

An object of this invention, therefore, is to provide an industrially eflicient process for the low temperature distillation of normally gaseous substances, particularly wherein one fraction is employed as a circulating heat transfer medium for the recovery of refrigerant and energy values.

Another object of this invention is to fractionate air in a simple and economical manner so as to simultaneously produce, in addition to the compressed oxygen, other components in liquid form.

Other objects and advantages of the present invention will become apparent upon further study of the specification and appended claims.

The objects of this invention are achieved by causing the circulating nitrogen which has been taken from the top of the pressure column to absorb heat indirectly from the air that is to be cooled, and/or from compressed nitrogen. This heated circulating nitrogen is then compressed to a high pressure (about 1.5 to 3 times the pressure of the gaseous high pressure oxygen to be produced), and a portion thereof (about 20-90%) is passed through heat exchangers for transferring its heat to the evaporating oxygen. The other portion (about 10-80%) of the compressed circulating nitrogen, after precooling is then partially (about /2) allowed to expand while doing external work, and is thereafter released into the pressure column. The remaining part of said other portion of the compressed circulating nitrogen may simultaneously with said first portion be recycled to the top of the pressure column by way of an expansion device after being cooled by products and circulation nitrogen respectively which have been already withdrawn from the double column.

3,216,26 Patented Nov. 9, 1965 The preferred embodiment of this invention is depicted in fiowsheet form in the attached drawing.

The energy gain and refrigeration resulting from the work producing expansion of a portion of the highly compressed condensed circulating nitrogen is so great that considerable quantities of the separated nitrogen and oxygen fractions can be obtained in liquid form without the use of supplemental refrigeration, for example, 50% of the oxygen in the feed and 25% of the nitrogen in the feed.

A considerable portion (about 40-60% of the oxygen in the feed) of the liquefied oxygen which has collected in the sump can be removed while in the liquid state, without evaporating it by absorption of the heat from the air to be fractionated. This is advantageous because the production of liquid oxygen and likewise the production of liquid nitrogen are important for various reasons such as the storage of larger quantities and the transport of larger amounts.

Furthermore, it is also possible and especially advantageous here to obtain especially pure oxygen in a supplementary column which can be heated by the circulating nitrogen of a corresponding pressure stage.

Similarly, a considerable portion (about 20-30% of the nitrogen in the feed) of the nitrogen in the air can advantageously be obtained in the liquid state from the upper part of the high pressure column (about 5.5-6.5 atmospheres absolute).

For the production of especially pure nitrogen, some of the nitrogen which has been taken from the upper portion of the high pressure column (about 40-60% of the nitrogen in the feed) is introduced into a supplemental rectification column from the head of which pure liquid nitrogen is removed, While the liquid from the sump of this column is returned to the head of the high pressure column. The head condenser of the supplemental column is then advantageously cooled by a portion of the expanded oxygen from the sump of the high pressure column (about 30-50% of the oxygen in the feed), which portion is then returned to a distributing device in the middle of the low pressure column (about 1.3 atmospheres absolute). An additional refrigeration can be advantageously accomplished by expanding the gaseous nitrogen from the high pressure column in a work-performing turbine to a pressure of about 1.2 atmospheres absolute. For this purpose, a portion of the gaseous nitrogen from the top of the high pressure column (about 5-25% of the nitrogen in the feed, this portion depends on the quantity of liquid nitrogen withdrawn) is preheated by regenerative heat exchange with air to be fractionated and/ or by recuperative heat exchange with compressed circulation nitrogen and is passed through an expansion turbine, and combined with gaseous nitrogen from the head of the low pressure column (together at least about 70% of the nitrogen in the feed depending on the liquid nitrogen withdrawn). The remainder of this gaseous mixture is then passed in part (about 50%) through a regenerator intermittently and alternately with a countercurrent of the air to be fractionated, and in part through a heat exchanger in countercurrent relation to a current of compressed nitrogen, and then finally to the high pressure compressor.

In this installation comprising indirect heat exchange between the entering air and the nitrogen from the low and high pressure column, the sublimation of impurities, for example CO can be further improved by diverting a portion of the circulating nitrogen from the regenerator (about 20-40%), and passing it through a heat exchanger in countercurrent relation to the highly compressed nitrogen, and then returning it to the circulating nitrogen which leaves the regenerator.

Without further analysis, it is believed that one skilled in the art can readily appreciate and practice this invention. The following preferred embodiment, therefore, is not to be considered limitative of the remainder of the specification and appended claims in any way whatsoever.

The preferred embodiment of this invention, relating to a method of fractionating air, will now be described in detail, with particular reference to the attached drawmg.

Compressed air is delivered by a pipe 1 to one of the cyclically interchangeable regenerators la-ld and passes through the pipe 2 into the lower part of the high pressure distillation column 3 having about 20 plates. This column, however, can be omitted or have for example 40 plates. This depends on the desired purity and quantity of the products. From the bottom of this column impure oxygen is removed through the pipe 4, while from the upper portion of this column considerably enriched nitrogen is removed through pipes 5 and 6. head of the high pressure column there is a main condenser 7 which at the same time serves as a reboiler for the sump liquid of the low pressure column 8.

In the space 9 around the cooling tubes of the main condenser 7, liquid oxygen collects. The impure oxygen from pipe 4 is delivered selectively to one or the other of two alternately operated adsorbers 10 which also may be omitted, and from there through pipe 11, heat exchanger 12, and pipe 13, to be divided between two expansion valves 14 and 15, the valves 14 leading to the middle portion of the low pressure column 8 having about 45 plates (this column may also have 5 or 85 plates depending on the desired purity and quantity of the products), while the valve 15 leads through pipe 16 to the condenser 17 of a supplementary nitrogen rectification column 18, from which the vaporized impure oxygen passes through the pipe 19 into the middle portion of column 8 at a somewhat lower level. Into the supplementary column 18 having about 20 plates, nitrogen is introduced via pipe 5. (This column, however, can be omitted or have for example 40 plates. This depends on the desired purity and quantity of the products.) From the sump of the column 18 liquid oxygen-containing nitrogen is returned through pipe 20 to column 3. The liquid nitrogen which collects on the highest tray 21 is conducted by pipe 22 to the expansion valve 23, for delivery into the upper end of the column 8 where it is received momentarily by the distributor 25 for use as a wash liquid, and preferably with intermediate cooling and expansion. Gaseous nitrogen is delivered from the upper end of column 8 through pipe 26 to the heat exchanger 12, and from there through pipe 27 and manifold 28 to two branch pipes 29 and 30 leading to two of the regenerators 1a-1d from which the gaseous nitrogen is then delivered by pipes 31, 32 for outside use.

Very pure liquid nitrogen is delivered from the highest tray 33 of supplementary column 18 through pipe 34 to a tank 35, from which it can be drawn off through the pipe 36 for outside use. Liquid oxygen is removed from the main condenser through pipe 37 and tank 38 to the discharge pipe 39, from which it can be obtained for outside use.

Another portion of the liquid oxygen is removed through pipe 41 for delivery to the high pressure pump 42, from which it is'delivered under pressure to the heat exchanger 43a, from there through pipe 44 to heat exchanger 44a, from there through pipe 45 to heat exchanger 45a, and finally in the form of gaseous oxygen under pressure to the pipe 46 for outside use.

The above-mentioned pipe 6 delivers considerably enriched nitrogen to one of the regenerators la-ld, e.g. 1d, or through the branch pipe 48 to the heat exchanger 43b. From the heat exchanger 43b the nitrogen passes through pipe 49 to the heat exchanger 45b, then through pipe 50 to heat exchanger 45c, and from there through P p 51 10 the Same p p 2 which receives the nitrogen At the I,

from the regenerator 1d. The pipe 52 then conducts its nitrogen to the high pressure pump 53 which is preferably of the dry type to avoid any possibility of oil being carried by the compressed nitrogen into the heat exchangers where it could cause explosions.

The nitrogen which is thus compressed to 50-200 atm., depending on what liquefied fractions are needed, is conducted through pipe 54 and branch pipes 55 and 56 to the above-mentioned heat exchangers 450 or 45a. Pipe 57 delivers the nitrogen from heat exchanger 450 to heat exchanger 45b and from there to heat exchanger 44a through one tube, while the pipe 59 delivers the nitrogen from heat exchanger 45a to heat exchanger 44a through another tube. These two tubes are coupled respectively to pipes 60 and 61 which lead to heat exchangers 43b and 43a respectively. The pipes 62 and 63 conduct the highly cooled nitrogen from the heat exchangers 43b and 43a to the expansion valves 64 and 65 respectively, and from there through pipes 66 and 67 to the head of the pressure column 3.

A branch pipe 69 leads from pipe 49 for delivering a portion of the nitrogen to an expansion turbine 70 which exhausts into the pipe 71 connected to the manifold 28 connected to two of the regenerators la-ld. Some of the nitrogen may then be returned from the regenerator 1d through pipe 72 to pipe 49.

Some of the compressed and precooled nitrogen may be removed from pipes 57 and 59 and conducted through pipe 73 to the expansion turbine 74 and from there through pipe 75 to pressure column 3.

The external Work performed by turbines 74 and 70 amounts to about 140 kcaL/Nm O withdrawn in liquid state and kcaL/Nm N withdrawn in liquid state.

With this invention the cost of an installation for the production of gaseous compressed oxygen, liquid oxygen and liquid nitrogen will be about 10% less than with previously known installations, the reason being that (1) oxygen compressors and (2) supplementary recycling compressors for further cooling are avoided. The operating cost is also appreciably reduced thereby.

The process of this invention can be appropriately modified for the separation of gas mixtures other than air, as for example, mixtures of hydrocarbons such as natural gas. For that purpose, the most abundant compo nent, such as methane, could be used instead of nitrogen as the circulating medium.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the present invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. In a process for producing compressed gaseous oxygen by the low temperature rectification of air in a double rectification column having a bottom high pressure column and a top low pressure column wherein circulating nitrogen is utilized as a heat transfer medium, and wherein at least a portion of liquefied oxygen from the bottom of the low pressure column is compressed and then passed in heat transfer relationship with the circulating nitrogen, said oxygen being thereby vaporized, the improvement which comprises (1) withdrawing a nitrogen enriched stream from the top zone of the high pressure column, (2) preheating said stream by heat exchange partly with air to be separated and partly with a portion of said stream after being compressed, (3) compressing said prehated nitrogen enriched stream, (4) expanding at least a portion of said nitrogen enriched stream through an expansion turbine to produce external work after being precooled by said heat exchange, (5) recycling the resultant expanded nitrogen stream to the high pressure column, (6) simultaneously passing a second portion of thecornpressed nitrogen enriched stream in heat exchange relationship with at least one low temperature fraction from the double column, thereby cooling the second nitrogenenriched stream, and (7) expanding the resultant cooled second stream into the top Zone of the high pressure column.

2. The process of claim 1, further comprising the step of withdrawing a portion of liquefied oxygen from the bottom of the low pressure column directly from the process in the liquefied state.

3. The process of claim 1, further comprising the step of withdrawing a portion of liquefied nitrogen directly from the process in the liquefied state.

4. The process of claim 1, further comprising the steps of withdrawing a gaseous nitrogen enriched stream from the top of the high pressure column, passing said stream to the bottom Zone of an additional fractionating column, fractionating said nitrogen enriched stream to pro duce a pure liquid nitrogen overhead product and an impure liquid bottom product, removing the pure liquid nitrogen product directly from the process, and recycling the impure liquid bottom product to the top zone of the high pressure column.

5. The process of claim 4, further comprising the steps of withdrawing an impure liquid oxygen stream from the bottom of the high pressure column, expanding said oxygen stream, passing the resultant expanded oxygen stream through the top of the additional fractionating column in indirect heat transfer relationship with the vapors therein, thereby actuating as condenser cooling liquid, and passing the resultant heated oxygen stream to the low pressure column for further fractionation.

6. The process of claim 1, further comprising the steps of preheating a portion of the circulation nitrogen in the lower part of a regenerator provided in a regenerator arrangement for cooling the air to be fractionated and combining the resultant preheated circulation nitrogen with a portion of said nitrogen enriched stream from the high pressure column after being preheated by heat exchange with compressed circulation nitrogen, and expanding the resultant nitrogen enriched stream through a second expansion turbine to produce external work; combining the resultant expanded nitrogen enriched stream with gaseous nitrogen from the top Zone of the low pressure column; passing the combined streams through regenerators of said arrangement alternately and countercurrently to the air to be fractionated; passing a portion of the circulation nitrogen in countercurrent heat exchange relationship to compressed circulation nitr-ogen, and then compressing both of said resultant portions of the circulation nitrogen to produce compressed circulation nitrogen.

7. The process of claim 6, further comprising the steps of diverting some of the circulation nitrogen before passing completely through the regenerator, to a heat exchanger; passing the diverted circulation nitrogen through said heat exchanger in indirect countercurrent relationship with compressed circulation nitrogen, thereby cooling said compressed circulation nitrogen and heating the diverted circulation nitrogen; and then combining the heated diverted circulation nitrogen together with the remaining circulation nitrogen having passed completely through the regenerator; and compressing to a high pressure the latter combined streams.

8. An apparatus for separating a gaseous mixture into fractions comprising; a circulation nitrogen compressor having an inlet and an outlet side, two heat exchangers having inlet and outlet sides, first conduit means connecting the outlet side of said compressor to the inlet side of the two heat exchangers, an expansion turbine means having an inlet and an outlet side, further a plurality of other heat exchangers having one flow path means for compressed circulation nitrogen and extending in one direction and other flow path means extending in the opposite direction for oxygen to be evaporated and heated respectively and circulation nitrogen from the top zone of the high pressure part of the double rectification column to be preheated before compression, a second conduit means connecting the outlet side of at least one of said two heat exchangers to the inlet side of the expansion turbine means and also to the inlet end of said one flow path means of said plurality of other heat exchangers, a double rectification column with a first high pressure and a second low pressure part and having inlet means in the said first part, third conduit means connecting the outlet side of the expansion turbine means to the inlet means of the high pressure part of the double rectification column; an expansion device; a fourth conduit means connecting the outlet end of said one flow path means of said plurality of heat exchangers via said expansion device to the inlet means of the high pressure part of the double rectification column; an arrangement of regenerators, each having a cold end and a warm end for cooling the air to be fractionated and for heating gaseous nitrogen as a product and to be recirculated respectively, and connecting conduits leading to and from said regenerators for conveying said air and nitrogen.

9. An apparatus for separating a gaseous mixture into fractions comprising; a circulation nitrogen compressor having an inlet and an outlet side, two heat exchangers having inlet and outlet sides, first conduit means connecting the outlet side of said compressor to the inlet side of the two heat exchangers, an expansion turbine means having an inlet and an outlet side, second conduit means connecting the outlet side of at least one of said heat exchangers to the inlet side of the expansion turbine means, a double rectification column having a first high pressure and a second low pressure part and third conduit means connecting the outlet side of the expansion turbine means to the inlet means of the double rectification column; further a plurality of heat exchangers for heat exchange between said compressed circulation nitrogen to be cooled and oxygen to be evaporated and heated respectively and circulation nitrogen from the upper zone of the high pressure part of said double rectification column to be preheated before compression, and an arrangement of regenerators, each having a cold and a warm end for cooling the air to be fractionated and for heating gaseous nitrogen as a product and to be recirculated respectively, and connecting conduits for said purposes; another heat exchanger connected for effecting heat exchange between circulation nitrogen to be preheated and compressed circulation nitrogen to be cooled; further a second expansion turbine the inlet of which is connected to the conduit for the nitrogen to be preheated at the outlet of said other heat exchanger and to a conduit di- Verting circulation nitrogen from a middle part of a regenerator of said regenerator arrangement; and the outlet of said second expansion turbine being connected by conduit means to the cold end of at least one regenerator of said arrangement.

References Cited by the Examiner UNITED STATES PATENTS 2,526,996 10/50 Crawford 6229 2,918,802 12/59 Grunberg 62-29 3,034,306 5/62 Schuftan 6241 X 3,083,544 4/63 Jakob 6241 3,100,696 8/63 Becker 6238 X 3,110,155 11/63 Schuftan 6241 NORMAN YUDKOFF, Primary Examiner. 

1. IN A PROCESS FOR PRODUCING COMPRESSED GASEOUS OXYGEN BY THE LOW TEMPERATURE RECTIFICATION OF AIR IN A DOUBLE RECTIFICATION COLUMN HAVING A BOTTOM HIGH PRESSURE COLUMN AND A TOP LOW PRESSURE COMUMN WHEREIN CIRCULATING NITROGEN IS UTILIZED AS A HEAT TRANSFER MEDIUM, AND WHEREIN AT LEAST A PORTION OF LIQUEFIED OXYGEN FROM THE BOTTOM OF THE LOW PRESSURE COLUMN IS COMPRESSED AND THEN PASSED IN HEAT TRANSFER RELATIONSHIP WITH THE CIRCULATING NITROGEN, SAID OXYGEN BEING THEREBY VAPORIZED, THE IMPROVEMENT WHICH COMPRISES (1) WITHDRAWING A NITROGEN ENRICHED STREAM FROM THE TOP ZONE OF THE HIGH PRESSURE COLUMN, (2) PREHEATING SAID STREAM BY HEAT EXCHANGE PARTLY WITH AIR TO BE SEPARATED AND PARTLY WITH A PORTION OF SAID STREAM AFTER BEING COMPRESSED, (3) COMPRESSING SAID PREHATED NITROGEN ENRICHED STREAM, (4) EXPANDING AT LEAST A PORTION OF SAID NITROGEN ENRICHED STREAM THROUGH AN EXPANSION TURBINE TO PRODUCE EXTERNAL WORK AFTER BEING PRECOOLED BY SAID HEAT EXCHANGE, (5) RECYCLING THE RESULTANT EXPANDED NITROGEEN STREAM TO THE HIGH PRESSURE COLUMN, (6) SIMULTANEOUSLY PASSING A SECOND PORTION OF THE COMPRESSED NITROGEN ENRICHED STREAM IN HEAT EXCHANGE RELATIONSHIP WITH AT LEAST ONE LOW TEMPERATURE FRACTION FROM THE DOUBLE COLUMN, THEREBY COOLING THE SECOND NITROGENENRICHED STREAM, AND (7) EXPANDING THE RESULTANT COOLED SECOND STREAM INTO THE TOP ZONE OF THE HIGH PRESSURE COLUMN. 